On 28/09/2021 05:23, Dan Mahoney (Gushi) wrote:
Hey all,
I'm dealing with rc.d scripting and reading
https://docs.freebsd.org/en/articles/rc-scripting/
Here's my question: Is there a sane way to have something like foo_pid
*completely unset* in one case, but overridable by rc.conf after?
It took me a bit to wrap my head around the:
: ${dummy_enable:=no}
: ${dummy_msg="Nothing started."}
Examples. (Why that first colon, what is this := syntax), etc.
The first colon is builtin function same as /bin/true
A useful application for : is if you're only interested in using
parameter expansions for their side-effects rather than actually passing
their result to a command.
You can use the parameter expansion as an argument to :
: "${var:=$1}"
There is as many variants to handle this as many rc scripts are
installed on your system. Each have it slightly different (syntax) but
with the same meaning:
Apache
[ -z "$apache24_enable" ] && apache24_enable="NO"
[ -z "$apache24limits_enable" ] && apache24limits_enable="NO"
[ -z "$apache24limits_args" ] && apache24limits_args="-e -C daemon"
[ -z "$apache24_http_accept_enable" ] && apache24_http_accept_enable="NO"
[ -z "$apache24_configcheck_disable" ] && apache24_configcheck_disable="NO"
Amavisd
: ${amavisd_enable:=NO}
pidfile=${amavisd_pidfile-"/var/amavis/amavisd.pid"}
ISC DHCPD
# default name to "dhcpd" if guessing failed
# Trailing semicolon also for service(8)'s benefit:
name="${name:-dhcpd}" ;
name=${name##*/isc-}
Some more explanation:
To get the assigned value, or default if it's missing:
FOO="${VARIABLE:-default}"
Or to assign default to VARIABLE at the same time:
FOO="${VARIABLE:=default}"
Or check the link
https://bash.cyberciti.biz/guide/Default_shell_variables_value
What I'm trying to say in rc.subr language is:
If the user has set something in rc.conf, use it. Otherwise, leave it
TOTALLY UNSET. Not to the null string. Undefined.
Easily readable syntax can be like this:
[ -n "$kdc_pid" ] && pidfile="$kdc_pid"
Variable pidfile will be set to a value of $kdc_pid only if $kdc_pid is
set and is not empty.
Miroslav Lachman
